For porous substrates to be used for tiles, concrete, inorganic construction materials and old (deteriorated) coating walls and the like, treatment of forming resin coatings on the surfaces of substrates has mainly been carried out in order to reinforce or fill substrate surface layers. As a sealer to be used in such a case, in general, solvent type sealers have conventionally been used. However in recent years, use of organic solvents tends to be restricted more strictly and shift to water-based coating materials is desired. In such a situation, it has been required to develop water-based sealers comprising emulsions.
So far, as water-based sealers, the following have been proposed: for examples, as described in Japanese Kokai Publicaion Hei-10-310739, water-based undercoating agent which comprises a water-based medium and copolymer dissolved therein and obtained by copolymerizing monomer mixtures containing (a) 8 to 70% by weight of an ethylenic unsaturated carboxylic acid, (b) 30 to 92% by weight of at least one monomer selected from a group consisting of acrylic acid or methacrylic acid ester with alkyl having 1 to 18 carbon atoms, aromatic vinyl compound, vinyl halide, saturated carboxylic acid vinyl ester, acrylonitrile, methacrylonitrile, ethylene, and butadiene, and (c) 0 to 20% by weight of other monomers and which are characterized in that 30% or more of the above-mentioned ethylenic unsaturated carboxylic acid (a) exists in neutralized state by addition of an alkali and as described in Japanese Kokai Publication 2000-204285, water-based sealer containing, as basic resin component, water-based mixed resin solution of synthetic resin emulsion (I) and water-soluble resin solution (II). Also, as resin compositions suitable for water-based indoor coating material, there are proposed resin composition for water-based coating material, as described in Japanese Kokai Publicaiton Hei-11-343464, each comprising (A) a water-based emulsion of copolymer having a lowest film formation temperature and a glass transition temperature in respectively specified ranges and (B) a resin having a glass transition temperature in a specified range and made solubilized in water by an alkali and weight ratio A/B on the basis of non-volatile components in (A) and (B) being in a range of 95/5 to 60/40.
However, the above-mentioned conventionally known water-based sealers contain, as main components, polymers with high water solubility in order to keep high impregnating adhesion property. Therefore, as compared with conventionally widely employed solvent type sealers, there is a disadvantage that they are considerably inferior in water penetration resistance.
Further, in conventional techniques essentially using a water-soluble resin and an emulsion, the particles in the emulsion are relatively large in general and coatings are formed by filling gaps among large particles with the water-soluble resin and such coating is provided only with insufficient water permeation resistance as compared with solvent type sealers in present situation. To say more particularly, conventionally, it has been well known that the particle diameter of particles in an emulsion can be controlled to be small by increasing the amount of a surfactant, but on the other hand, it also has been well known that the existence of a large quantity of a surfactant causes decrease of water penetration resistance and in the case of aiming to improve the water penetration resistance, making the particle diameter of an emulsion small by using a large quantity of a surfactant has been supposed to be rather disadvantageous in terms of water penetration resistance. Additionally, in conventional techniques essentially using a water-soluble resin and an emulsion, selective use of alkali-soluble one as the water-soluble resin may be possible to improve the water penetration resistance, however water penetration resistance as high as that of a solvent type sealer has not been obtained yet.
Accordingly, it has been required to improve the water penetration resistance of a water-based sealer to be as high as that of a solvent type sealer and to satisfy the requirement, it has been desired to develop an emulsion which can form a coating excellent in water penetration resistance as well as impregnating adhesion property.